COTTON-BASED ELASTICISED YARNS TO MAKE ENVIRONMENT-FRIENDLY ELASTICISED FABRICS

Abstract

A method is disclosed for making an elastic core yarn (50), wherein an elastic core (30) comprising a fibre (10) of natural rubber with metric count 200-1000 dtex is covered by a cotton-based covering yarn (40), comprises a step of conveying the elastic core (30) and the covering yarn (40) in such a way that the covering yarn (40) laterally attains a proximity of the elastic core (30) in a wrapping space (35); a step of helically wrapping the covering yarn (40) about the elastic core (30) in a wrapping space (35), wherein the conveying speed, and therefore the winding/unwinding speed, is selected such that the elastic core (30) is stretched up to a stretching ratio of at least 2, and such that, during this wrapping step, the covering yarn (40) becomes twisted with a final twist direction opposite to its initial twist direction, and forms a number T of coils per length unit of the elastic fibre (10) set between a predetermined minimum value T.sub.0 and a predetermined maximum value T.sub.1 both depending on the linear mass density Nm of covering yarn (40), the wrapping space (35) being enclosed by a container (67). An elasticised yarn obtained this way, and a fabric, in particular a denim type fabric, manufactured from this yarn.

Claims

1. A method for making an elastic core yarn (50) comprising the steps of: prearranging a source (51) of an elastic core (30) comprising an elastic fibre (10) made of a natural rubber containing more than 80% of cis-1,4-polyisoprene, wherein said elastic fibre (10) has a linear mass density set between 200 dtex and 1000 dtex; prearranging at least one covering yarn (40) comprising cotton at a weight percentage higher than 50%, wherein said covering yarn has a linear mass density set between 6 Nm and 100 Nm, said covering yarn (40) twisted with an initial twist direction selected between “Z” and “S”; conveying said elastic core (30) and said covering yarn (40) up to a collecting spool (70), at respective predetermined conveying speeds, wherein said conveying speed of said elastic core (30) speed ranges from an initial speed, at said source (51) of elastic core (30), to a final speed at least twice said initial speed, at said collecting spool (70), wherein said step of conveying is carried out in such a way that said covering yarn (40) laterally attains a proximity of said elastic core (30) in a wrapping space (35); helically wrapping said covering yarn (40) about said elastic core (30) in said wrapping space (35), thus obtaining said elastic core yarn (50); wherein said conveying speeds are selected in such a way that, in said step of helically wrapping: said covering yarn (40) becomes twisted with a final twist direction opposite to said initial twist direction, i.e. selected between “S” and “Z”, respectively; a number T of coils of said covering yarn (40) set between a predetermined minimum value T.sub.0 and a predetermined maximum value T.sub.1, said minimum and maximum values T.sub.0,T.sub.1 depending upon said linear mass density Nm, is wrapped about one length unit of said elastic core yarn (50), wherein said wrapping space (35) is a protected space enclosed by a container (67).

2. The method according to claim 1, wherein, for each linear mass density value Nm indicated in a respective line of the following table (table 1): TABLE-US-00003 N.sub.m T.sub.0 T.sub.1 6 100 800 8 120 850 10 150 950 16 180 1000 25 200 1200 30 220 1300 36 250 1500 42 300 1600 50 350 1650 76 450 1900 100 500 2100 said minimum and maximum values T.sub.0, T.sub.1 are the values written in said respective line and in the columns headed by T.sub.0 and T.sub.1, respectively, of said table, for values of said linear mass density Nm intermediate between values indicated in respective contiguous lines of said table, said minimum and maximum values T.sub.0,T.sub.1 are obtained by linearly interpolating the values written in said respective contiguous lines and in the columns headed by T0 and T1 of said table, respectively.

3. The method according to claim 2, wherein said number T of coils per length unit, for each value of said linear mass density Nm, has a value provided by the equation:
T=K Nm.sup.0.425; where K is a number set between 75 and 290.

4. The method according to claim 3, wherein in particular, K is set between 90 and 250.

5. The method according to claim 3, wherein more in particular, K is set between 120 and 220.

6. The method according to claim 1, wherein said covering yarn (40) is selected among a single-ply yarn, a double-ply yarn and a yarn having more than two plies.

7. The method according to claim 1, wherein said step of conveying said elastic core (30) and said covering yarn (40) up to said collecting spool (70) comprises: steps of causing said elastic core (30) and said covering yarn (40) to travel through a longitudinal through cavity (63) and along a lateral surface (62), respectively, of a rotating hollow cylindrical body (61) turning at a predetermined rotation speed, said longitudinal through cavity (63) having an inlet end opening (68) and an outlet end opening (69) for said elastic core (30); a step of causing said elastic core (30) and said covering yarn (40) to pass through an orifice (66) facing said outlet end opening (69) of said longitudinal through cavity (63) of said hollow cylindrical body (61) at a predetermined distance therefrom, and wherein said wrapping space (35) is set between said outlet end opening (69) and said orifice (66), such that said container (67) has an outlet passageway at said orifice (66) and said elastic core (30) and said covering yarn (40) pass through said orifice (66) as said elastic core yarn (50).

8. The method according to claim 1, wherein said source of said elastic core (30) is a spool (51) comprising a central hub (53) having a hub radius (r) and end flanges (54) having a flange radius (R), said spool (51) rotatably arranged about an own first axis (52), and said step of conveying said elastic core (30) comprises a step of unwinding said elastic core (30) from said spool (51), wherein an intermediate balancing cylinder (56) having a predetermined radius (P) longer than said flange radius (R) shortened by said hub radius (r) has a fixed own second axis (57) parallel to said first axis (52), and is arranged at contact between said spool (51) and a motion distribution shaft (58) parallel to said first and second axes (52,59), whereby, during said step of unwinding, said elastic core (30) is maintained in contact with said intermediate balancing cylinder (56).

9. The method according to claim 1, wherein said elastic fibre (1) also comprises the following components: a vulcanisation agent, wherein said vulcanisation agent is sulphur at a weight concentration in said natural rubber set between 0.5% and 3.0%; a vulcanization accelerator and a vulcanization activator; an anti-tacking agent; an antioxidant agent; a stabilisation agent, and said elastic fibre (1) is obtained from a longitudinally cut flat yarn of said natural rubber, so as to obtain said elastic fibre (1) in the form of an elastic filament having said linear mass density.

10. The method according to claim 1, wherein said elastic core (30) comprises a complementary thread (20) arranged along said elastic fibre (10).

11. The method according to claim 10, wherein said complementary thread (20) is made of a biodegradable material.

12. The method according to claim 11, wherein said biodegradable material is selected from the group consisting of: wool, silk, cotton, flax, hemp, jute, sisal, raffia, ramie.

13. The method according to claim 10, wherein said complementary thread (20) is a continuous thread having an arrangement along said elastic fibre (10) selected from the group consisting of: an parallel arrangement, wherein said complementary thread (20) is arranged parallel to said elastic fibre (10); an interconnected arrangement, wherein said complementary thread (20) has connection points to said elastic fibre (10), said connection points arranged at a predetermined distance from each other; an wrapped arrangement, wherein said complementary thread (20) forms a covering about said elastic fibre (10),

14. The method according to claim 13, wherein said complementary thread (20) is selected between a single-filament continuous thread and a multiple-filament continuous thread comprising flat or textured filaments.

15. An elastic core yarn made by the method according to any of claims 1 to 14.

16. An elasticised denim fabric containing the elastic core yarn according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention will be now shown with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings, in which:

[0057] FIG. 1 diagrammatically shows a step of helically wrapping the covering yarn about the elastic core comprising an elastic fibre to obtain an elasticized yarn in the form of an elastic core yarn;

[0058] FIG. 2 diagrammatically shows a device for carrying out the step of helically wrapping the covering yarn about the elastic core, in an exemplary embodiment;

[0059] FIGS. 3 and 4 are diagrammatical side views of an unwinding unit for unwinding the elastic fibre of a twisting element, the unwinding unit comprising an intermediate balancing cylinder;

[0060] FIG. 5 shows the unwinding unit FIGS. 3 and 4 in three different instants of the unwinding step, i.e. at the beginning (a), at the end (c) and in an intermediate instant (b) of the unwinding step;

[0061] FIG. 6 is a diagram showing how the minimum, maximum, reference number of coils depend on the metric count of the covering yarn;

[0062] FIG. 7 diagrammatically shows a step of helically wrapping the covering yarn about an elastic core comprising a complementary thread in addition to the elastic fibre;

[0063] FIG. 8 diagrammatically shows a device for carrying out the step of helically wrapping the covering yarn about the elastic core of FIG. 7.

DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

[0064] With reference to FIG. 1, a method is described for making an elastic core yarn 50, wherein an elastic core 30 is coated by a covering yarn 40 helically arranged about elastic core 30. The method provides a step of prearranging elastic core 30, which comprises an elastic fibre 10 made of natural rubber, and typically having a linear mass density set between 200 dtex and 1000 dtex. The method also comprises a step of prearranging a cotton-based covering yarn 40 that has a metric count Nm and is twisted with a predetermined initial twist direction, which can be “Z” or “S”, and typically “Z”, as normally available in the trade.

[0065] Elastic core yarn 50 is obtained by a step of covering by helically wrapping covering yarn 40 about elastic core 30. In order to accomplish the wrapping, steps are provided of conveying elastic core 30 and covering yarn 40 at respective speeds v.sub.1 and v.sub.2, to a wrapping space 35, where covering yarn 40 laterally i.e. tangentially attains elastic core 30, covering yarn 40 at a predetermined angle α with respect to elastic core 30 when attaining the latter, so as to form a substantially helical covering about elastic core 30.

[0066] Wrapping space 35 is a normally closed space, as shown in FIG. 2, so that covering yarn 40 is turned from a substantially linear arrangement, when entering into wrapping space 35, to a helically wrapped arrangement, in a reduced-turbulence environment, in order to limit the friction of elastic core 30, of covering yarn 40 and of yarn 50 with air, during the wrapping step.

[0067] As also shown in FIG. 2, the steps of conveying elastic core 30 and covering yarn 40 are controlled by a speed v.sub.3 at which elastic core yarn 50 is collected on a collecting spool 70. As a consequence, covering yarn 40 and elastic fibre 10 are withdrawn from respective sources, which can be such storage devices as spools 41, 51.

[0068] As also shown in FIG. 2, in an exemplary embodiment, the step of conveying elastic core 30 towards wrapping space 35 is carried out through a central longitudinal through cavity 63 of a first cylindrical body 61 arranged to quickly rotate, at a predetermined rotation speed, about its own axis 63′, then elastic core 30 is conveyed along a substantially linear path. Instead, the step of conveying covering yarn 40 is carried out along an outer surface 62 of first cylinder 61, preferably along a guide element arranged thereon, not shown. Preferably, first cylindrical body 61 is housed integrally and coaxially within a second hollow cylinder 64, creating a conveying unit 60. Spool 41 of covering yarn 40 is integrally arranged within second cylindrical body 64, such that the step of conveying covering yarn 40 takes place in a gap 65 between spool 41 and the outer surface of first cylindrical body 61.

[0069] In this exemplary embodiment, wrapping space 35 is defined between an outlet end 69 of first cylindrical body 61, at which elastic core 30 is delivered, and an orifice 66 that is preferably arranged along axis 63′, from which elastic core yarn 50 is released in a stretched condition, to be in turn conveyed to collecting spool 70. The covering of wrapping space 35 is made by a preferably axisymmetric wall 67′ converging from an inner surface of second hollow cylindrical body 64 to orifice 66, thus creating a container 67, of which orifice 66 is an outlet passageway for elastic core yarn 50 formed within wrapping space 35.

[0070] Conveying speeds v.sub.1 and v.sub.2 (FIG. 1) of elastic core 30 and covering yarn 40, respectively, as well as the rotation speed of conveying unit 60, are selected in such a way that, in the step to helically wrapping covering yarn 40 about elastic core 30, covering yarn 40 changes its own twist direction, for instance from “Z” to “5”, and in other words becomes twisted with a final twist direction opposite to an initial twist direction, turning from a Z-twisted covering yarn 40Z into an S-twisted covering yarn 40S. Moreover, speeds v.sub.1 and v.sub.2 are selected in such a way that a number T of coils set between a predetermined minimum value T.sub.0 and a predetermined maximum value T.sub.1 is wrapped about each length unit of newly-manufactured elastic core yarn 50, maximum and minimum values T.sub.0,T.sub.1 depending on metric count Nm of covering yarn 40.

[0071] Source 51 of elastic core 30 can be a spool 51 of elastic fibre 10 rotatably arranged about its own axis 52 and comprises a central hub 53 and end flanges 54 of radius R, at end portions of central hub 53 of radius r, as shown in FIG. 4. Spool 51 is moved by a motion distribution shaft 58, i.e. a cylinder 58 that is rotatably arranged about an own rotation axis 59 throughout an array of of aligned twisting units of a twisting machine. To this purpose, rotation axis 59 of motion distribution shaft 58 is parallel to (common) rotation axis 52 of (each) spool 51, and motion distribution shaft 58 is arranged in contact with the free surface of unwinding elastic fibre 10, as also shown in FIG. 2, in order to cause spool 51 to rotate at a prefixed rotation speed.

[0072] In a preferred embodiment of the invention, as shown in FIGS. 3 to 5, an intermediate balancing cylinder 56 is arranged between motion distribution shaft 58 and spools 51 of elastic fibre 10 of the twisting units, with its own axis 57 parallel to axis 52 of spools 51 and axis 59 of motion distribution shaft 58. More in detail, intermediate balancing cylinder 56 is freely rotatably arranged in contact with the surface of motion distribution shaft 58, on one side, and in contact with the surface of spool 51, on another opposite side, i.e. it is arranged in contact with the free surface of unwinding elastic fibre 10. Cylinder radius P of intermediate balancing cylinder 56 is longer than flange radius R, shortened by hub radius r, i.e. the relationship

P>R−r

is verified.

[0073] Axis 52 of spool 51 is slidingly arranged along a guide 55 integral to the spinning machine. This way, as the unwinding step progresses, the amount of elastic fibre 10 on spool 51 decreases, and therefore axis 52 along with spool 51 progressively approach intermediate balancing cylinder 56 and therefore approach motion distribution shaft 58, as shown in FIG. 5. In a vertical arrangement of the unwinding unit, in which spool 51 is arranged above motion distribution shaft 58 as in FIGS. 3 and 4, the relative approach movement of spool 51 and intermediate balancing cylinder 56 is possible due to gravity acting on spool 51. In other cases, but preferably also in this case, a spring means, not shown, can be advantageously provided for progressively recalling spool 51 to motion distribution shaft 58 as the step of unwinding elastic fibre 10 progresses.

[0074] Therefore, as shown in FIG. 5, while being unwound, elastic filament 10 is always withdrawn from spool 51 at a same distance L=S+2P, regardless the unwinding state of coil 51, where S (FIG. 3) is the radius of motion distribution shaft 58. This way, no periodic adjustments of tensile force acting on elastic fibre 10 are required to maintain the stretching ratio of elastic fibre 10 at a fixed value, preferably between 2 and 6, and to maintain the number of coils actually wrapped about the core at a fixed value, provided winding speed v.sub.3 is maintained at a fixed value, gradually as the step of unwinding progresses.

[0075] The material of the covering yarn is a cotton-based material based on cotton, in particular it contains at least 50% cotton. For instance, this material can be a material normally used for making a denim fabric. The cotton-based covering yarn can be a single-ply yarn, a double-ply yarn or even a yarn having more than two plies.

[0076] FIG. 6 is a diagram showing the predetermined minimum value T.sub.0 of number T of coils to be wrapped about a length unit of elastic core yarn 50 being manufactured, for each linear mass density value Nm of covering yarn 40, in the form of a curve 81. Curve 81 is obtained by interpolating the values of the middle column of table 1.

[0077] The diagram of FIG. 6 also shows a curve 82 indicating, for each linear mass density value Nm of covering yarn 40, a maximum number T.sub.1 of coils that can be wrapped without losing the elastic properties of elastic core yarn 50, as experience has shown. Curve 82 is obtained by interpolating the values of the right column of table 1.

[0078] Advantageously, the number T of coils per length unit of elastic core yarn 50, for each value Nm of metric count of covering yarn 40, is provided by the equation:

T=K Nm.sup.0.425;

where K is a number set between 75 and 290, these values substantially corresponding to curves 83 and 84 of the diagram of FIG. 6. More in particular, K can be set between 90 and 250, more in particular, between 120 and 220.

[0079] The diagram of FIG. 6 also shows a band 85 corresponding to preferred values T of number of coils per length unit, set between ±10% a central reference value T.sub.2 that is obtained by interpolating the values of table 2, corresponding to curve 86.

[0080] With reference to FIGS. 7 and 8, elastic core 30 can also comprise a complementary thread 20 arranged along elastic fibre 10. In this case, the step of prearranging elastic core 30 provides steps of prearranging a fourth spool, not shown, of complementary thread 20, and the step of conveying the elastic core involves, besides elastic fibre 10, also complementary thread 20. A friction wheel 15 can also be provided to which elastic fibre 10 and complementary thread 20 converge, before being conveyed together into central longitudinal through cavity 63, through an inlet opening 68 thereof, of first cylindrical hollow object 61.

[0081] Preferably, complementary thread 20 is made of a biodegradable or compostable material that can be, for instance, wool, silk, cotton, flax, hemp, jute, sisal, raffia, ramie.

[0082] Complementary thread 20 can be a discontinuous or continuous filament, in the latter case it can be a single-filament continuous thread or a multiple-filament continuous thread. The filament or the filaments thereof can be flat or textured filaments.

[0083] Still in the case of a continuous complementary thread 20, FIG. 7 only shows a substantially parallel arrangement, in which complementary thread 20 and elastic fibre 10 are parallel to each other. However, the invention is not limited by this exemplary embodiment, since different arrangements between complementary thread 20 and elastic fibre 10 are possible, such as a wrapped arrangement, in which complementary thread 20 forms a covering about elastic fibre 10, as well as an interconnected arrangement, in which connection point are provided between complementary thread 20 and elastic fibre 10, at predetermined distance from each other.

[0084] It falls within the scope of the present patent application an elastic core yarn manufactured by the method described above, also an elasticised fabric containing such an elastic core yarn.

[0085] The foregoing description exemplary embodiments of the invention will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications the embodiments without further research and without parting from the invention, and, accordingly, it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation.